Such a method is discussed in the printed document Liebscher P.: “Aktuelle Trends bei der Steuergeräte-Reprogrammierung” (Current trends in the reprogramming of control units) in: Elektronik automotive 2.2006, pp. 34-37. The patent document DE 10 2008 052 955 A1, not previously published, also refers to the transmission of program codes to a memory of a control unit in which initially the program memory in the control unit is overwritten with invalid codes, subsequently, the program codes to be transmitted are compressed in accordance with the Huffman data compression method, transmitted, decompressed in the control unit and stored.
The printed document Decker, Th.: “Lecture &: Huffman”; in: Online library Wikipedia, 19.01.1999, http://www.itec.uka.de/seminare/redundanz/vortrag06/ (seminars/redundancy/lecture06/) and US 2007/0016406 A1, DE 39 43 881 B4 and DE 699 16 661 T2 discuss that the Huffman coding can be optimized by using as data words to be coded not only individual input data words but pairs/tuples of these input words.
Patent documents US 2007/0016406 A1 and DE 39 43 881 B4, additionally discuss switching over the Huffman codings used in dependence on the data currently to be coded, and this is done area-by-area within the data to be coded. Furthermore, a code bit for distinguishing between different coding variants is provided in DE 39 43 881 B4.
To transmit relatively large quantities of data within a justifiable time, it is known to compress the data to be transmitted. The very efficient loss-free Huffman coding is suitable for this purpose. The Huffman 16 coding, which operates with 16-bit data words, is very efficient but requires a relatively large coding tree for decoding (up to approx. 278 Kbytes). The size depends on the code utilization. Each 16-bit code used costs 34 bits in the coding tree for decoding. Correspondingly, the generation of the coding tree also takes a long time. In addition, the coding tree also has to be transmitted during the data transmission for the decoding and, due to its size, may no longer fit into the main memory of the destination system or control unit, respectively.
On the other hand, the Huffman 8 coding, which operates with 8-bit data words, manages with a smaller coding tree for the decoding (approx. 574 bytes) but does not achieve the efficiency of the Huffman 16 coding.